JP2003197214A - SEPARATOR PLATE MATERIAL MADE OF HIGH STRENGTH Ni GROUP ALLOY FOR SOLID HIGH POLYMER FUEL CELL, HIGH IN CONTACT SURFACE CONDUCTIVITY FOR LONG PERIOD OF TIME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator plate material made of a high strength Ni group alloy for a solid high polymer fuel cell, which has contact surface conductivity over a long period of time. <P>SOLUTION: The above separator plate material of the solid high polymer type fuel cell, which is constituted by pressing and assembling a plurality of power generating modules while piling it up mutually, which has the structure that the separator plate material, in which the anode is sandwiched on one side surface of a solid high polymer electrolyte film and while contacting this, a fuel gas flow way is formed, and on the other side surface of it, the separator plate material, in which, the cathode is sandwiched, and while contacting this, an oxidizing gas flow way is formed, is constituted with the Ni group alloy, which has the composition, which consists of containing Fe: 25 to 35%, Cr: 15 to 25%, Ti: 0.1 to 3%, and B: 0.01 to 1%, by mass % and the remainder that has Ni and unavoidable impurities, and the organization, which has the metallic boride distributed in decentralized distribution on a foundation of austenite. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell which exhibits excellent contact surface electrical conductivity over a long period of time without deterioration over time and has high strength. The present invention relates to a separator plate made of a Ni-based alloy for a polymer electrolyte fuel cell (hereinafter, simply referred to as a fuel cell) which enables a reduction in thickness which is indispensable for weight reduction and size reduction. 2. Description of the Related Art Conventionally, in general, the above-mentioned fuel cell is shown in FIGS.
As shown in the above, a single power generation module called a single cell has a structure in which a plurality of single power generation modules are stacked and pressed and assembled, and the single cell is sandwiched on one side of a solid polymer electrolyte membrane with an anode (hydrogen electrode) interposed therebetween. A separator plate is in contact with the separator, and the other side of the solid polymer electrolyte membrane is also in contact with a separator plate across a cathode (an oxygen electrode or an air electrode). It is well known that a fuel gas passage is formed on the contact surface, and an oxidizing gas passage is formed on the contact surface with the cathode. Further, in the above fuel cell, a hydrogen gas at about 80 ° C. normally flows through a fuel gas flow path formed on the anode side of the separator plate, and an oxidizing gas flow path on the cathode side is connected to the air at about 80 ° C. It is also known that a power generation function is exhibited by flowing a mixed gas with water vapor, which is a reaction product of the above. Furthermore, as described above, the cathode contact surface of the fuel cell separator plate is
The cathode is exposed to an oxidizing gas flow of a mixed gas of steam and air at about 80 ° C. When an oxide film is formed on the cathode contact surface, the contact surface conductivity is significantly reduced, and the battery Various materials having excellent corrosion resistance are used for forming the separator plate material because it causes deterioration of the function. Among such materials, as a material showing good corrosion resistance, mass% (hereinafter,% is In addition, the Ni-based alloy having an austenitic single phase structure, which contains Fe: 25 to 35% and Cr: 15 to 25%, and has a balance of Ni and unavoidable impurities, has been noted.
A fuel cell separator plate made of this Ni-based alloy has been proposed. On the other hand, there is a strong demand for higher performance of fuel cells in recent years, and accordingly, separator plates, which are structural members of the fuel cells, are required to be used under severer corrosion conditions. Although there is a tendency to be forced, even in the case of the conventional Ni-based alloy separator plate having good corrosion resistance,
Insufficient corrosion resistance under severe corrosive conditions, the electrical conductivity of the contact surface decreases over time, and inevitably leads to a shorter service life in a relatively short time. Also, as a result, the separator plate is also strongly required to be reduced in thickness.However, if the thickness is reduced too much, the contact resistance between the single cells is reduced as described above.
That is, for the purpose of ensuring good contact surface conduction,
With the fact that it is practically used in a state of being tightened and pressed at a pressure of about 3 MPa, plastic deformation occurs due to insufficient strength, and it is not possible to achieve a sufficiently satisfactory thinning. . [0004] Accordingly, the present inventors have proposed:
In view of the above, the above-described conventional Ni-based alloy separator plate material having particularly good corrosion resistance was focused on, and as a result of conducting research to improve the corrosion resistance and the strength of the conventional Ni-based alloy separator, N that constitutes the plate material
Ti and B (boron) are contained as alloy components in the i-base alloy, Fe: 25 to 35%, Cr: 15 to 25%, Ti: 0.1 to 3%, B: 0.01 to 1%, When the separator plate is composed of a Ni-based alloy having a composition consisting of Ni and unavoidable impurities, the resulting Ni-based alloy separator plate has a Ni-based alloy comprising an austenitic base material. Has a structure in which metal borides having a size of about 0.5 to 10 μm in a length direction are dispersed and distributed, and the metal borides are more susceptible to the above-mentioned oxidizing gas flow path atmosphere than the base austenite. Since it exhibits extremely excellent corrosion resistance and has excellent conductivity, the oxidation of the austenite of the base material progresses, and even if the contact surface electrical conductivity of the base material decreases over time, metal The boride ensures excellent contact surface conduction for a long period of time. Further, the base strength is significantly improved by solid solution of Ti and B components. The research results show that the material exhibits excellent plastic deformation resistance even below. The present invention has been made based on the above research results, and has a separator in which a fuel gas channel is formed on one side of a solid polymer electrolyte membrane with an anode interposed therebetween and in contact with the anode. The plate member is formed by laminating a plurality of single power generation modules each having a structure in which a separator plate member having an oxidizing gas passage formed in contact with the cathode material is sandwiched on the other side surface, and is pressed and assembled. In the fuel cell, the separator plate material contains Fe: 25 to 35%, Cr: 15 to 25%, Ti: 0.1 to 3%, and B: 0.01 to 1%, with the remainder being inevitable with Ni. A high-strength Ni-base alloy for a fuel cell that exhibits excellent contact surface conduction over a long period of time and is composed of a Ni-base alloy having a composition of impurities and a structure in which metal boride is dispersed and distributed in an austenite base. Those characterized by a separator plate. Next, the reason why the composition of the Ni-base alloy constituting the separator plate of the present invention is determined as described above will be described. (A) Fe In the Fe component, a base austenite is formed together with the Ni and Cr components to improve rolling workability and form a metal boride having excellent corrosion resistance and conductivity, which is dispersed and distributed in the base. Has the effect of maintaining excellent contact surface electrical conductivity for a long period of time.
If it is less than 5%, a desired improvement effect cannot be obtained in the above-mentioned action,
On the other hand, if the content exceeds 35%, the corrosion resistance rapidly decreases, so the content is set to 25 to 35%. (B) Cr For the Cr component, as described above, the base austenite is formed together with Ni and Fe to improve the corrosion resistance of the base, and also the metal boride dispersed and distributed in the base is formed. However, if the content is less than 15%, a desired improvement effect cannot be obtained in the above-mentioned action, while if the content exceeds 25%, the rolling process is performed. The content is determined to be 15 to 25% because the property is lowered. (C) Ti A part of the Ti component forms a solid solution with the austenite of the base material to improve the strength, and the main part forms a metal boride as described above to form a contact surface with a conductive material. In addition to contributing to the improvement, there is an effect of promoting the formation of the metal boride, but if the content is less than 0.1%, the desired effect cannot be obtained in the above-mentioned effect, while the content is 3%. If the content exceeds 0.1%, the rolling processability will decrease.
It was determined as 1-3%. (D) BB A small part of the B component forms a solid solution in the matrix and contributes to the improvement of the strength of the matrix, but most of the B component has a diameter of 0 in the length direction as described above. Forming metal boride with excellent corrosion resistance and conductivity distributed in a size of 0.5 to 10 μm,
It has the effect of suppressing the deterioration over time of the electrical conductivity of the contact surface and maintaining an excellent power generation function over a long period of time.
If the content is less than 01%, the formation of metal borides is insufficient and the above-mentioned effects cannot be obtained, and if the content exceeds 1%, the formation of metal borides becomes too large, resulting in poor rollability. Since the tendency to decrease appears, the content is set to 0.01 to 1%. Next, the separator plate of the present invention will be specifically described with reference to examples. As raw materials, high-purity Ni and Fe materials each having a purity of 99.9% or more,
Cr material, Ti material, and Ni-B mother alloy material (B: 17%
), And melted with a vacuum high-frequency induction melting device to prepare a molten metal having a predetermined component composition, and cast this into a water-cooled copper mold to form a plate-shaped ingot having a thickness of 5 mm.
This plate-shaped ingot was repeatedly subjected to hot rolling at a rolling start temperature of 1200 ° C. four times to obtain a hot-rolled sheet having a thickness of 2 mm, and then held at 1150 ° C. for 10 minutes and then cooled with water. After treatment and holding at 500 ° C. for 10 minutes, an air-cooled tempering treatment was performed, and after pickling, the thickness was 1 mm by cold working.
From 10 mm to 0.1 mm by 0.1 mm at a time, and these cold-rolled sheets were kept at 500 ° C. for 10 minutes, subjected to air-cooling heat treatment, and pickled to a thickness of 50 mm.
A 50 mm x 50 mm plate is cut out, and four grooves having a width of 5 mm and a depth of 3 mm corresponding to the fuel gas flow path and the oxidizing gas flow path are formed in parallel at the center of the plate at 5 mm intervals. In this way, separator plates 1 to 17 of the present invention and conventional separator plates 1 to 9 each made of a Ni-based alloy having a component composition shown in Tables 1 and 2 were produced. The structures of the various separator plates obtained as a result were examined with a scanning electron microscope (1000
2), the separator plate material 1 of the present invention was observed.
Indicates a structure in which metal borides having a size of 0.5 to 10 μm in a length direction are dispersed and distributed in an austenite base, and conventional separator plate materials 1 to 21 are each composed of an austenite single phase. The organization showed. Next, for the purpose of evaluating the strength of the above-mentioned various separator plates, the above-mentioned 10 types of separator plates having different thicknesses were each subjected to a plane dimension of 150 mm × 150 mm.
mm, thickness: 4 MPa corresponding to the pressure for assembling a single cell constituting a fuel cell from above in a state where the stainless steel plate is horizontally sandwiched between 3 mm stainless steel plates from above and below.
The sheet pressure was applied, and the sheet was taken out after holding for 1 minute, and the sheet thickness at which plastic deformation occurred in the press-formed groove of the separator sheet (plastic deformation occurrence sheet thickness) was measured. The measurement results are shown in Tables 1 and 2. In order to evaluate the change with time of the contact surface electrical conductivity of the above-mentioned various separator plates, the size of the above-mentioned various separator plates having a thickness of 30 mm was evaluated.
A test piece of × 30 mm was cut out, and silicon carbide abrasive grains having a grain size of 180 were sprayed on the surface of the test piece using a compressed air nozzle at a pressure of 0.5 MPa to form fine irregularities on the surface, and contact was made. In order to increase the surface area,
Atmosphere equivalent to the oxidizing atmosphere to which the oxidizing gas flow path of the separator plate is exposed after etching for 1 minute with a 20% HCl aqueous solution of 20 ° C., thoroughly washed with boiling ion-exchanged water, and completely dried. That is, a corrosion test was performed for 1000 hours, 2000 hours, and 3000 hours in an atmosphere of saturated water vapor at 80 ° C., and the contact electric resistance after the corrosion test was measured. In addition, the contact electric resistance value was set as a set of the above test pieces: two pieces, and they were superposed on each other with a 0.3 mm thick carbon paper sandwiched therebetween. A DC current of 15 A was passed in a state where the test piece was pressurized at a pressure of 3 MPa, a potential difference between the test pieces was measured, and a contact electric resistance value was calculated from the measured potential difference. The results are also shown in Tables 1 and 2. In this case, the lower the contact electric resistance value indicates that the contact surface electrical conductivity after the corrosion test on the surface of the separator plate material is excellent, and conversely, the higher the contact electric resistance value after the corrosion test, the higher the contact electric resistance value becomes. This indicates that the contact surface conductivity is low. [Table 1] [Table 2] According to the results shown in Tables 1 and 2, all of the separator plates 1 to 17 of the present invention are formed by the presence of a metal boride having excellent corrosion resistance and conductivity which is dispersed and distributed in an austenitic base material. Even if the austenite of the base material is oxidized and the contact surface electrical conductivity at this portion decreases, good contact surface electrical conductivity can be ensured for a long time through the metal boride, and further contained as an alloy component. Since high strength is ensured by solid solution of Ti and B in the base material, plastic deformation hardly occurs even if the thickness is reduced, but the metal boride is not formed, and Ti and B In the conventional separator plates 1 to 9 having no solid solution, the entire surface oxide film is formed by the oxidation of the austenite single phase, so that the contact surface conductivity decreases with time and the contact electric resistance value does not increase with time. It is clear that plastic deformation tends to occur due to insufficient strength, and satisfactory thinning cannot be achieved. As described above, the separator plate material of the present invention exhibits excellent contact surface electrical conductivity for a long period of time, and has high strength that enables thinning. This greatly contributes to weight reduction and miniaturization.

[Brief description of the drawings] FIG. 1 is a schematic perspective view of a fuel cell. FIG. 2 is a partially exploded perspective view of the fuel cell.

Claims (1)

Claims: 1. A separator plate having a fuel gas passage formed in contact with one side of an anode on one side of a solid polymer electrolyte membrane, and a cathode on the other side of the solid polymer electrolyte membrane. In a polymer electrolyte fuel cell, a plurality of single power generation modules each having a structure in which a separator plate member in which an oxidizing gas flow path is formed in contact with and sandwiching the same are superimposed and assembled by pressure welding. The plate material contains, by mass%, Fe: 25 to 35%, Cr: 15 to 25%, Ti: 0.1 to 3%, and B: 0.01 to 1%, with the balance being Ni and inevitable impurities. Characterized by comprising a Ni-based alloy having a structure in which a metal boride is dispersed and distributed in an austenitic base,
A high-strength Ni-based alloy separator plate material for polymer electrolyte fuel cells that exhibits excellent contact surface conductivity over a long period of time.